1. Field of the Invention
The present invention relates to a planar antenna with a cover. More specifically, the present invention relates to a planar antenna for a radar level meter or a microwave barrier system.
2. Description of the Related Art
A planar antenna for a radar level meter is known from DE 198 00 306 A1, the contents of which are incorporated herein by reference, in which an axial HF input is achieved by means of planar radiator elements (patch antennas) arranged on a substrate at the end face of a waveguide.
There are applications in level measurement where detrimental high temperature or high pressure can occur and the planar antenna can also be exposed to a chemically corrosive atmosphere.
Therefore, in the related art, the planar radiator elements arranged on a substrate are covered with a sheet of ceramics or PTFE (polytetrafluorethylene, such as Teflon), in order to achieve in particular an adequate chemical resistance. Such a planar antenna is shown schematically in FIG. 12. Here, a planar radiator element 102 is arranged on a circuit board 101 as the substrate and covered flush with the surface by a PTFE cover 201. But this has highly negative influence on the HF properties of the individual planar radiator elements, in particular, only a slight bandwidth is available. Moreover, the cover also has great influence on the patch geometry. Unfortunately, detriments remained.
In order to improve the HF properties of the antenna and the chemical resistance, WO 2007/124860 A1, which is incorporated herein by reference, proposes placing a planar radiator element directly on the back side of such a cover, separating the region outside the planar antenna from the region inside it in the way of a process separation, such a cover being made from ceramics or glass. Thanks to this arrangement of the radiator element inside the antenna, a good seal against the surroundings, i.e., the process surroundings, can be achieved. Unfortunately, the drawback, is the use of ceramics or glass, since this leads to very high costs in production, especially in regard to the mounting and the necessary sealing work.
Finally, it is also known how to arrange the cover with a distance of half a wavelength of the microwaves or a multiple thereof in front of the planar radiator element. But, again unfortunately, this has the effect of greatly reducing the pressure bearing ability and therefore one must again resort in disadvantageous manner to harder and more pressure-stable materials like glass or ceramics, so that as already mentioned above the manufacturing costs of such a planar antenna rise considerably.
Thus, the inventors have recognized the problem and have proposed a solution so as to indicate a planar antenna of the kind mentioned at the outset, having an improved construction and thus being easy to produce, without having the above-mentioned disadvantages. In particular, such a planar antenna should be able to withstand a high process pressure.
Accordingly, there is a need solved by a planar antenna with a cover with the features of proposed invention including an adaptive radar level meter or microwave barrier, as well as other systems.